As noted in the earlier application, an apparatus for the construction of tunnels and shafts and, more particularly, a mine gallery excavator can have a leading ring or shield, and a follower or trailing ring or shield, wherein the two rings or shields can be united to form a unitary shield structure by a joint connection. The leading shield can carry the excavator head which is advanced with the leading shield by hydraulic jacks or piston and cylinder arrangements braced by the machine rearwardly thereof. After a certain degree of advance of the tunnel or gallery, these jacks draw the trailing shield forwardly and casing sections can be introduced behind the trailing shield and concrete pumped into the clearance defined between the casing and the excavated tunnel wall.
The apparatus also can include therefore at least one pressure ring, a plurality of advancing piston/cylinder assemblies, and a roll correction device. The advancing piston/cylinder assemblies are distributed about the shield circumference, and they are connected by way of linkages to the pressure ring.
The advancing piston/cylinder assemblies are also supported by way of linkages at the leading shield. The roll correction device has adjusting piston/cylinder assemblies by means of which the inclination of the advancing piston/cylinder assemblies can be adjusted with respect to the longitudinal axis of the generatrices of the shield.
I have found that under conditions of nonhomogeneous soil, ground or rock, hereinafter generally referred to as surrounding formation, as well as in the case of structural changes of the apparatus, there is little one can do to prevent torque reactions at the body of the shield.
Furthermore, torque reactions can not be avoided at the shield, at least when drilling into rock and other ground in full-cut fashion with rotating tools, and rotary motions are experienced about the longitudinal axis of the shield. Such movements are referred to as roll, rolling or revolving out-of-true, and include similar twisting or gyrating motions, and misalignments.
Such undesired movements affect the leading shield and the follower or trailing shield, individually and jointly. These undesirable movements are particularly critical when using a follower ring which is linked to a respective component by a movable connection which is formed by piston/cylinder arrangements, because such piston/cylinder assemblies allow only limited relative roll movements.
In apparatus which has found practical application, heretofore, the roll correction device cooperates with the pressure ring. Auxiliary means provided by adjusting piston/cylinder assemblies, which are correspondingly supported or braced, serve to rotate the pressure ring about its axis with respect to the precursor ring. This rotation causes the inclination of the advancing piston/cylinder assemblies which are directly mounted at the precursor shield, and torque is created at a cost of only a slightly reduced longitudinal advancing force, when the advancing force is applied which produces the respective inclined component. In this way, the torque which would cause a twisting or gyrating motion can be generally compensated. As well, a leading shield which does not operate as desired can be controlled.
The described rotation of the pressure ring is not easily achieved and requires a certain disturbance of the respective adjoining region. During operation of the advancing piston/cylinder assemblies, the pressure ring according to one prior art embodiment must be adjustable for roll correction.
Separate rotation of the pressure ring is not feasible when the pressure ring is connected to the follower shield so as to rotate therewith. Such connection is customarily employed and is preferred.
A simple correction of the relative roll or offset motion between the precursor shield and the follower shield cannot be achieved actively in prior art equipment.